How to prepare a PDF for print, and the 8 mistakes that get your file sent back

Contents

1. What it means for a PDF to be print-ready
2. The missing bleed
3. The resolution that is not what you think
4. RGB when the press prints in CMYK
5. The safety margin and the cut-off text
6. Fonts: embedded, not lost
7. Special finishes that are not separated
8. The wrong format and the wrong size
9. The checklist before you send it
10. Who should check all this

What does it mean for a PDF to be print-ready?

Preparing a PDF for print means delivering a file that holds up through the physical process that comes next: the cut, the resolution the paper demands and the inks loaded on the press. A PDF that looks perfect on screen can be useless on press, and that confusion is behind almost every rejected file. The screen forgives. The guillotine does not.

The practical difference is this: a screen file only has to look right. A print file has to survive being cut with a millimetre of drift, being enlarged to its real size, having its colours translated into four inks and having its fonts exist on a computer that is not yours.

The mistakes that get a file sent back are almost always the same eight, and we have watched them repeat themselves job after job for years. None of them is exotic. All of them are measurable, which is the important part: either the bleed is there or it is not, either the image reaches 300 dots per inch at its final size or it does not. There is no opinion involved.

Why is bleed always missing, and why is it 3 mm?

Bleed is the artwork that extends past the trim line, usually three millimetres on each side. It exists because no guillotine cuts with absolute precision: there is a tolerance of a millimetre or so, and if the artwork ends exactly on the trim line, that drift leaves a white strip at the edge. With bleed, the drift eats spare artwork and nobody notices.

The classic mistake is not forgetting the bleed, it is believing you added it. Setting the document up with three millimetres of bleed in your design software does nothing if the colour background stops exactly at the edge of the page. Bleed has to be drawn: the background, the photo and the colour block have to physically extend into those extra three millimetres.

• Bleed: the artwork that extends beyond the cut to absorb the guillotine's drift. Standard: 3 mm per side.
• Trim line: the final size of the piece, where it is actually cut.
• Safety margin: the inward cushion where nothing important should sit.

For books, packaging or large format, the printer may ask you for five millimetres or more. It is a two-second question that prevents a rejection.

What resolution do your images really need?

The standard print resolution is 300 dots per inch (DPI) at the final printed size, and that last part is where almost everyone falls down. A 300 dpi image that you place at twice its size ends up with a real 150 dpi. The file still says 300 in its metadata, but what reaches the press is 150, and it shows.

That is where the two most common resolution mistakes come from:

• The stretched web image: a photo downloaded from a website, 800 pixels wide, placed at 20 centimetres. On screen it looks acceptable. Printed, it looks mushy, with soft edges.
• The silent enlargement: a correct image that someone scales up in the layout without recalculating. Nobody touches the original file, so nobody suspects anything.

In large format the rule changes, and for the better. A banner seen from ten metres away does not need 300 dpi: much less is used, because the viewing distance is forgiving. What never changes is that resolution has to be measured at the output size, not at the size of the file.

RGB or CMYK? The conversion someone is going to do for you

Screens emit light and work in RGB. Printing presses lay down ink and work in CMYK, with four inks: cyan, magenta, yellow and black. They are two different colour spaces, and the second one is smaller: some colours exist on your screen and do not exist in ink, and nothing can be done about it.

What matters is not that the conversion happens, because it is going to happen anyway. What matters is who does it. If you send the PDF in RGB, the conversion will be done by the printer's system with a profile you did not choose, and electric blues and saturated greens will turn dull without anyone telling you. If you do it yourself, with the profile your printer gives you, you see the result before it is printed and decide whether it works for you.

Black deserves a paragraph of its own. The default black in many applications is flat black, K ink only, and in a large area it looks washed out, almost a dirty grey. For backgrounds and large surfaces a rich black is used, which adds some cyan, magenta and yellow underneath the black. For small text, on the other hand, use flat black: a rich black at 8 points multiplies the risk of the four inks not lining up and the text coming out with coloured edges.

What is the safety margin, and why does it cut off your text?

The safety margin is the cushion towards the inside of the piece, usually between three and five millimetres from the trim line, where nothing should sit that you cannot afford to lose. It is the sibling of bleed, pointing the other way: bleed protects the outer edge from white strips, and the safety margin protects the content from the guillotine.

It is the same cutting tolerance as before, seen from the other side. If the phone number on a business card sits one millimetre from the edge, all it takes is a millimetre of guillotine drift and you lose the last digit. And with business cards you do not lose one: you lose the whole run.

The rule is simple: nothing critical near the edge. No text, no logos, no codes, no signatures. And the cut is not the only threat: on a bound product, the spine also swallows several millimetres of the page.

Should fonts be embedded or converted to outlines?

Embedding a font means putting the characters needed to draw the text inside the PDF. Converting to outlines means you no longer have text, you have geometric shapes. The correct default is to embed: it is what any modern workflow expects and what the PDF/X standard requires.

The failure happens when neither of the two occurs. The PDF goes out with a reference to a font that exists on the designer's computer and nowhere else, and in prepress it is replaced with another one. The text is still there and still readable, which is why this one is so treacherous: nothing breaks, the line spacing simply shifts, a headline takes up one more line and the design stops being the one that was approved.

Converting to outlines fixes the problem at the root, but it comes at a price: the text stops being text. You cannot fix a typo without going back to the original file, search for a word or extract the content. It works as a plan B when the font licence does not allow embedding or when the printer asks for it, not as the default method.

How should special finishes be supplied?

A special finish (varnish, metallic foil, die cutting, embossing) is not ink: it is a physical process applied afterwards to the already printed paper. That is why it cannot be mixed into the artwork. It has to sit on its own separation, defined as a spot ink with a recognisable name and with overprint turned on.

The usual mistake is drawing the varnish area on top of the design, in black or in any CMYK colour. When that reaches the press there are two possible outcomes, and both are bad: either that shape is printed as if it were ink, ruining the sheet, or it is ignored and the job comes out without the finish the customer paid for.

This is by far the most expensive mistake on the list, because it is caught late and sometimes only once it is already printed. And it is exactly the kind of check a piece of software does in a second: looking at a PDF's list of separations and seeing whether the varnish is where it should be is trivial for a machine and tedious for a person.

What format and size should you send?

The format is PDF, with a surname: PDF/X. It is a subset of PDF defined by ISO specifically for graphic arts, which requires everything needed to print to travel inside the file (fonts, images, colour profiles) and forbids anything that makes no sense in print. Today the most widespread flavour is PDF/X-4, because it supports transparency and layers without having to flatten them. Adobe documents the export presets, and the Ghent Workgroup publishes reference specifications for each type of job.

Two practical notes that are forgotten more often than you would think, even in 2026:

• The artwork size has to be the real size. An A1 poster designed at A4 "so the file is lighter" reaches the press with a quarter of the usable resolution.
• One file, one job. A 12-page PDF when the job is a two-panel leaflet forces someone to guess what to print, and guessing in prepress is expensive.

The checklist before you send it

Who should check all this?

Whoever creates the file, because they are the only one who can fix it cheaply. A missing bleed takes two minutes to fix in the original document, and a couple of hours when someone tries to rebuild it from a closed PDF, without the layers, without the fonts and without knowing what was underneath that photo.

What actually happens is the opposite. The file is sent by email or WeTransfer, nobody looks at it, and the problem shows up on the prepress desk when the press slot is already booked. Then the chain every print shop knows begins: the emails back and forth with the customer, the job on hold, the delivery date eating into the margin and, quite often, the printer redoing for free artwork that is not theirs. We tell it in our story, because it is exactly the problem that made us build Entregarte.

And the curious thing is that almost nothing on this list requires judgement. The bleed is there or it is not. The image reaches 300 dpi or it does not. The varnish has its separation or it does not. These are measurable checks, and measurable checks are better done by software: always the same way, in seconds and without getting tired by the tenth file of the day.

That is the idea behind Entregarte's validations: the check happens at the moment the customer uploads the file, not two days later. If something fails, the customer sees it straight away, in plain language, and fixes it themselves, since they are the one who can. And if it passes, it reaches the print shop ready for the press. The final decision always stays with the print shop: the software informs, it does not reject jobs on its own.

The future of prepress is not a person checking PDFs one by one at nine in the evening. It is the broken file never reaching that desk. You can start your 7-day trial and have it validating your customers' files today, or tell us about your case if your workflow has something specific you would like to talk through first.